The present invention relates to a constant velocity universal joint which is used in the power transmission systems of automobiles and various industrial machines, and more particularly it relates to a slidable constant velocity universal joint which is capable of transmitting rotary motion at constant velocity even when driving and driven shafts to be joined together form an angle (operating angle) and which allows a relative axial movement between the driving and driven shafts.
As for slidable constant velocity universal joints used in the transmission systems of automobiles, for example, there are some known forms of the so-called tripod type. One form, as shown in FIGS. 9 and 10, comprises an outer joint member 21 having three track grooves 22 formed in its inner peripheral surface and extending axially of the outer joint member, and a tripod member 24 having three radially extending leg shafts 25 with rollers 20 rotatably fitted on the cylindrical outer peripheral surfaces thereof through rolling elements 26, said tripod member 24 being inserted in the outer joint member 21 with said rollers 20 fitted in the track grooves 22. Each roller 20 is received in the associated track groove 22 such that it is engaged with the roller guide surfaces 22a of the associated track groove 22 opposed to each other circumferentially of the outer joint member, said roller 20 being capable of moving axially of the outer joint member while rotating around the axis of the leg shaft 25.
When the outer joint member 21 and the tripod member 24 form a operating angle .theta. as shown in FIG. 11 during torque transmission, the roller 20 and the roller guide surface 22a of the track groove 22 are in mutually slanting relation as shown in FIG. 12. In this case, the roller 20 tends to move by rolling in the direction of arrow a in FIG. 11, and since the track groove 22 has a cylindrical form extending parallel to the axis of the outer joint member, the roller 20 moves while being constrained by the track groove 22. As a result, slippage occurs between the roller guide surface 22a of the track groove 22 and the roller 20 to produce heat, and such slippage induces an axial thrust force. Such induced thrust causes vibrations of the car body and noise and therefore should desirably be minimized.
There is known a tripod type constant velocity universal joint designed to reduce induced thrust and having rollers each constructed of a combination of inner and outer rings to make the joint oscillatable (Japanese Patent Publication 1991-1529). This joint, for example, as shown in FIGS. 13 and 14, includes inner rings 27 rotatably fitted on the cylindrical outer peripheral surfaces of the leg shafts 25 of the tripod member 24 through rolling elements 26, and outer rings 23 rotatably fitted on said inner rings 27. Each inner ring 27 has a truly spherical outer peripheral surface 27b around the axis of the leg shaft 25, and the cylindrical inner peripheral surface 23a of the outer ring 23 is rotatably fitted on said spherical outer peripheral surface 27b, whereby the outer ring 23 is made swingable with respect to the axis of the leg shaft 25. The outer rings 23 are received in the track grooves 22 of the outer joint member 21 and are capable of moving axially of the outer joint member while rolling on the roller guide surfaces 22a.
In this oscillating or swing type, when the outer joint member 21 and the tripod member 24 form a operating angle during torque transmission as shown in FIG. 15, the outer ring 23 is inclined with respect to the axis of the leg shaft 25, when the spherical outer peripheral surface 27b of the inner ring 27 relatively slides on the cylindrical inner peripheral surface 23a of the outer ring 23. This relative movement between the inner and outer rings 27 and 23 causes the outer ring 23 to be guided parallel to the axis of the outer joint member 21 by the roller guide surfaces 22a of the outer joint member 21, so that the outer ring 23 correctly rolls on the roller guide surfaces 22a; thus, the sliding resistance on the roller guide surfaces 22a is reduced and the generation of the induced thrust force is suppressed.
In this connection, in said oscillating constant velocity universal joint, during torque transmission at a operating angle, the relative sliding movement between the outer and inner rings 23 and 27 results in a sliding friction component in the direction of the axis of the leg shaft 25 acting on the outer ring 23. This frictional force changes its direction of action through 180.degree. at the ends of the stroke of said relative movement (when the phase angle is 0.degree. and 180.degree., respectively). That is, immediately before the outer ring 23 reaches the stroke end shown in FIG. 16 (the direction of rotation of the tripod member 24 being taken as clockwise), said frictional force F acts radially inward. Immediately after it has reached the stroke end shown in FIG. 17, however, the frictional force F is reversed to act radially outward. In the conventional article, since the center of curvature O of the spherical outer peripheral surface 23b of the outer ring 23 is located more inward than the cylindrical inner peripheral surface 23a, a clockwise moment M.sub.F around the sphere center O due to said frictional force F acts on the outer ring 23 immediately before the latter reaches the stroke end (see FIG. 16), while a counterclockwise moment M.sub.F around the center of curvature O acts on the outer ring 23 immediately after the latter has reached the stroke end (see FIG. 17).
Further, not only does the frictional force F act on the outer ring 23 but also a turning force P attending the torque transmission acts perpendicular to the cylindrical inner peripheral surface 23a. This turning force P acts always in a fixed direction, without changing the direction as does said frictional force F, with the result that a counterclockwise moment M.sub.P around the sphere center O always acts on the outer ring 23.
As is apparent from the foregoing description, the two moments M.sub.F and M.sub.P acting on the outer ring 23 act in opposite directions to cancel out each other immediately before the outer ring 23 reaches the stroke end (FIG. 16) but in the same direction immediately after it has passed by the stroke end (FIG. 17). Thus, the combined moment acting on the outer ring 23 suddenly changes before and after the stroke end, so that immediately after passing by the stroke end, the outer ring 23 inclines as shown in broken line in FIG. 17, a situation which could form a cause of generating an induced thrust or a sliding resistance.
There are various forms of said oscillating constant velocity universal joint as shown in FIGS. 18 through 21, and in each form, the center of curvature O of the spherical outer peripheral surface 23b of the outer ring 23 is deviated from the region S where a sliding movement in the direction of the leg shaft occurs; therefore, as in FIGS. 16 and 17, the outer ring 23 tends to exhibit unstable behavior at the stroke ends.
Accordingly, an object of the present invention is to prevent the outer ring from exhibiting such unstable behavior in specific phases.